Rename fls() to __fls()

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/fls.h b/fls.h
index 850859b..dc7ecd0 100644
--- a/fls.h
+++ b/fls.h
@@ -9,7 +9,7 @@
  * Note fls(0) = 0, fls(1) = 1, fls(0x80000000) = 32.
  */
 
-static inline int fls(int x)
+static inline int __fls(int x)
 {
 	int r = 32;